The present invention relates generally to corona charging devices for use in electrostatographic machines and more particularly to a grid electrode for connection to a corona charging device used in such machines.
Generally, the process of electrostatographic copying is executed by exposing a light image of an original document to a substantially uniformly charge photoreceptor member. Exposing the charge photoreceptor member to a light image selectively discharges the photoconductive surface thereof to create an electrostatic latent image of the original document on the photoreceptor member. The electrostatic latent image is subsequently developed into a visible image by a process in which charge developing material is deposited onto the photoconductive surface of the photoreceptor such that the developing material is selectively attracted to the image areas thereon. The developing material is then transferred from the photoreceptor member to a copy sheet on which the tone image may be permanently affixed to provide a reproduction of the original document. In a final step, the photoconductive surface of the photoreceptor member is cleaned to remove any residual developing material therefrom in preparation for successive imaging cycles.
The described process is well known and is useful for light lens copying from the original as well as the printing of documents from electronically generated or stored originals. Analogous processes also exist in other electrostatographic applications such as, for example, digital printing applications where latent images are generated by a modulated laser beam or LED print head.
In electrostatographic applications, it is common practice to use corona generating devices for providing electrostatic fields to drive various machine operations. Such corona devices are primarily used to deposit charge on the photoreceptor member prior to exposure to the light image for subsequently enabling toner transfer thereto. In addition, corona devices are used in the transfer of an electrostatic toner image from the photoreceptor to a transfer substrate, in tacking and detacking paper to or from the imaging member by applying a neutralizing charge to the paper, and, generally in conditioning the imaging surface prior to, during and after toner is deposited thereon to improve the quality of the xerographic output copy.
In order to control a voltage potential of electrostatic charge on the surface, such as a photoconductive (PC) surface, it is known to provide a grid electrode between the corona charger electrode(s) and the PC surface. The grid electrode provides a series of wires or narrow metal strips across the opening of the charger housing out of which opening corona ions arc free to travel from the one or more corona generating wire electrodes or strip electrodes in the corona charger housing to the PC surface. By electrically biasing the wires of the grid assembly to the voltage potential desired to be created upon the PC surface there can be provided charging of the PC surface to the level of the grid voltage even though voltage potential of the corona charger is considerably higher.
In known copier/duplicator products, the primary charger grid electrode is in close proximity with the film surface (less than 0.125 inches) to insure uniform charging performance. A ground stripe is located on one or both edges of the PC film loop to provide an electrical ground path to the film Q-layer. Due to film curl and the close proximity of the charger grid electrode, contact between the grid electrode and the film ground stripe can occur. This can cause problems:
a. Contact between the ground stripe and the grid will short out the grid causing a loss of grid voltage. This will result in the film voltage that is too low and image quality will be severely impacted. PA1 b. When the ground stripe and the grid are almost touching, an arc can occur between the two surfaces. On a low level, the arc creates electrical noise that can interfere with the logic of the machine. Momentary loss of grid voltage due to the arc can cause image quality degradation. A high-energy arc can damage the film surface requiring it to be replaced. PA1 a. The grid surface has been curved at the ends. The grid does not have to be in close proximity with the film over the film stripe since this is not in the active charging area. PA1 b. Insulate the grid surface in the area over the ground stripe with insulating tape. This has been done in known copier/duplicator products because the curved grid approach cannot be used due to the need to have an active cleaning system in place. The curved grid may not allow sufficient room for the cleaning mechanism.
This problem in the past has been solved in two ways.
However, the insulating tape is subject to damage during normal machine operation, and can wear away. At some point in time, arcing or shorting out of the grid will occur.
It is an object of the invention to improve upon the grid electrodes of the prior art.
The invention and its various advantages will become more apparent to those skilled in the art from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings